1. Field of the Invention
The present invention relates to a process for the production of salt. More particularly, it concerns a process according to which sodium chloride is crystallised by evaporation of a sodium chloride brine.
2. Background of the Art
A process which has been in use for a long time for manufacturing food-grade salt consists in heating a sodium chloride brine below its boiling point, in open basins or pans, of a low height, which have a large evaporation area ("Sodium Chloride", Kaufmann, Reinhold Publishing Corp., 1960, p. 262).
The salt obtained by this known process, usually called "pan salt", is generally in the form of coarse, non-uniform particles, translucent and glassy in appearance, which is easy to use and which is, consequently, valued by certain users, for example for salt-preserving methods.
However, this salt manufacturing process has the disadvantage of being too costly, since the efficiency of heating brines in the pans is, in fact, very low. It has the additional disadvantage of requiring plant which occupies a very large ground area.
To overcome the above-mentioned disadvantages of this known process it has also been proposed to process sodium chloride brines in multistage evaporators (op. cit., p. 205).
Compared to the process for manufacturing pan salt described earlier, the use of multistage evaporators, which generally operate at a reduced pressure, permits a considerable fuel saving and is, moreover, adaptable to plant which occupies a smaller ground area.
However, the salt obtained by this known process is completely different from pan salt in appearance; it is usually in the form of fine particles, matt and opaque in appearance, the uses of which do not generally correspond to those of pan salt.